Drug delivery devices have application where regular injection by persons without formal medical training occurs. This may be increasingly common among patients having diabetes where self-treatment enables such patients to conduct effective management of their disease. In practice, such a drug delivery device allows a user to individually select and dispense a number of user variable doses of a medicament.
There are basically two types of drug delivery devices: resettable devices (i.e., reusable) and non-resettable (i.e., disposable). For example, disposable drug delivery devices are supplied as self-contained devices. Such self-contained devices do not have removable pre-filled cartridges. Rather, the pre-filled cartridges may not be removed and replaced from these devices without destroying the device itself. Consequently, such disposable devices need not have a resettable dose setting mechanism. The present disclosure is in general applicable for both types of devices, i.e. for disposable devices as well as for reusable devices.
A further differentiation of drug delivery device types refers to the drive mechanism: There are devices which are manually driven, e.g. by a user applying a force to an injection button, devices which are driven by a spring or the like and devices which combine these two concepts, i.e. spring assisted devices which still require a user to exert an injection force. The spring-type devices involve springs which are preloaded and springs which are loaded by the user during dose selecting. Some stored-energy devices use a combination of spring preload and additional energy provided by the user, for example during dose setting. Further types of energy storage may comprise compressed fluids or electrically driven devices with a battery or the like. Although many aspects of the present disclosure are applicable for all of these types of devices, i.e. for devices with or without a drive spring or the like energy storage, the preferred embodiments require some kind of energy storage.
These types of delivery devices generally comprise of three primary elements: a cartridge section that includes a cartridge often contained within a housing or holder; a needle assembly connected to one end of the cartridge section; and a dosing section connected to the other end of the cartridge section. A cartridge (often referred to as an ampoule) typically includes a reservoir that is filled with a medication (e.g., insulin), a movable rubber type bung or stopper located at one end of the cartridge reservoir, and a top having a pierceable rubber seal located at the other, often necked-down, end. A crimped annular metal band is typically used to hold the rubber seal in place. While the cartridge housing may be typically made of plastic, cartridge reservoirs have historically been made of glass.
The needle assembly is typically a replaceable double-ended needle assembly. Before an injection, a replaceable double-ended needle assembly is attached to one end of the cartridge assembly, a dose is set, and then the set dose is administered. Such removable needle assemblies may be threaded onto, or pushed (i.e., snapped) onto the pierceable seal end of the cartridge assembly.
The dosing section or dose setting mechanism is typically the portion of the device that is used to set (select) a dose. During an injection, a plunger, spindle or piston rod contained within the dose setting mechanism presses against the bung or stopper of the cartridge. This force causes the medication contained within the cartridge to be injected through an attached needle assembly. After an injection, as generally recommended by most drug delivery device and/or needle assembly manufacturers and suppliers, the needle assembly is removed and discarded.
In known drug delivery devices, there may be an internal gap between parts of the drug delivery device after assembly which have to contact each other to ensure the delivery of the correct amount of the dose. The gap may be located between parts of the drive mechanism or between a part of the drive mechanism and e.g. the cartridge. This gap is a consequence of the tolerances associated with all the assembled parts and the requirement not to apply an undesirably high preload on the bung axially in the assembled drug delivery device, because too much preload would pressurize the drug in the cartridge and may cause it to leak, or may cause creep damage to plastic parts if they are loaded for significant periods of time during storage.
In a conventional drug delivery device, a priming operation is performed to ensure that the parts of the driving mechanism are moved to their predetermined position with respect to the other parts. Typically, the priming step has to be performed prior to the first use of the device to close a possible gap between the cartridge bung and the plunger and to overcome tolerances within the device. For the priming step, a user has to set a small dose and to dispense this dose while monitoring whether e.g. fluid leaves the device. This action has to be repeated until e.g. fluid actually leaves the device.
There is a risk of an underdose at least during the first use of the device if a user does not perform this priming step. Users who are unfamiliar with such drug delivery devices may fail to correctly prime their drug delivery device before dispensing the first dose. If this occurs, the correct volume of the drug may not be delivered in the first dose, as part of the dialed dose is needed to close up any gaps between parts in the mechanism.
EP 2 482 899 B1 discloses a manually operated drug delivery device with an assembly which can be adjusted during assembly of the device, preferably during final assembly after fitting the cartridge, to bring a piston rod in contact with a cartridge bung. This removes tolerance gaps from the assembly and eliminates the need for a priming operation which is undertaken by the user prior to delivery the first dose of drug. The assembly of this known device requires using a tool to move a first drive member with respect to a second drive member, thereby moving a piston rod towards a bung during an assembly action, and thereafter coupling the first drive member with the second drive member so that the movement of the first drive member with respect to the second drive member is prevented during a dose setting and delivery action.
WO 2014/036239 A2, WO 2010/112377 A1 and WO 2008/142394 A1 each disclose a drug delivery device comprising a spring loaded piston which is attached to a belt or tether retaining the piston against the force of the spring. One end of the belt is attached to a spool on a gear wheel which is in engagement with a worm gear driven by an electric motor. Actuation of the motor allows unwinding of the belt which in turn allows displacement of the piston by the spring. In addition, WO 2014/036239 A2 mentions a control unit with a sensor detecting slack in the belt or tether. Further a sensor and an encoder may be used to provide positional feedback, end-of-dose signal and error indication.
WO 2014/139918 A1 and WO 2011/039229 A1 each describe an assembly method for a drug delivery device, wherein the device comprises a threaded piston rod engaging a threaded drive sleeve. During assembly the drive sleeve is rotated thereby advancing the piston rod. The torque required for rotating the piston rod is measured to detect a sudden increase in torque when the piston rod contacts a bung in a cartridge. WO 2014/029682 A2 proposes a method for detecting snap engagement of a piston rod and a bung by a sudden change in force or torque required for piston rod displacement.